8 Stokes, on the Nature of the Rontgen Kays. 



longitudinal vibrations ; and the experiments by which, 

 as I conceive, the possibility of their polarisation has 

 now been established, go completely in the same direc- 

 tion, showing that they are due, assuming them to be 

 some process going on in the ether, to a transversal 

 disturbance of some kind. 



Now, the so-called cathodic rays are, as we may say, 

 the parents of the Rontgen rays. Consequently, if we 

 are to explain the nature of the Rontgen rays, it is 

 very important that we should have as clear ideas as 

 may be permissible of the nature of the cathodic 

 rays. Now, two views have been entertained as to 

 the nature of the cathodic rays. According to one 

 view, they are not rays of light at all, but streams of 

 molecules which are projected from the cathode, and, 

 if the exhaustion within the tube be sufficient, reach the 

 opposite wall. That was the idea under which Crookes 

 worked in his well-known experiments, and, so far as I 

 know, it is the view held by all physicists in this country. 

 Another opinion, however, has been published, and there 

 are some eminent physicists who favour it, especially, I 

 think, in Germany. According to this latter opinion, the 

 .cathodic rays are, like rays of light, some process going 

 on in the ether. The cathodic ray, coming from the 

 cathode towards the opposite wall of the tube, is invisible 

 as such if you look across it. There is in reality a faint 

 blue light ordinarily, but not necessarily, seen when you 

 look across it. Lenard, in his most elaborate and 

 remarkable experiments, succeeded in producing the 

 cathodic rays within a space from which the gas was 

 so very nearly completely taken away that, although 

 the cathodic rays passed freely through the space, there 

 was no appearance of the blue light when you viewed 

 their path transversely. They produced, however, the 

 ordinary effect of phosphorescence at the other end of 



